The clear width of the lattice opening is understood to mean, for example, the diameter for a circular-shaped opening and the spacing of the narrow sides for a rectangular opening.
From EP 1 230 166 B1, a filter device is known, which has a filter cartridge. In order to prevent the exit of filter material located in the filter cartridge in the form of granular material, a form-stable or a flexible flat-shaped structure is arranged in the cover area of the filter cartridge, which structure has a maximum pore size or mesh width of 300 μm in order to prevent an exit of micro particles of the granular material also.
During the starting phase of the filtration process, water must be capable of penetrating the filter cartridge and the air within the filter cartridge must be capable of escaping. With regard to this problem it is stated that, when using sieve-type flat-shaped structures, a minor back pressure already suffices to close the sieve pores. In fabric technology, the closing of the pores with a moist film is called sail formation.
The dome-shaped sieve-type flat-shaped structure, for example, can comprise a synthetic material fabric, wherein the sail formation in the upper part of the flat-shaped structure, where the air exits, is to be avoided by means of hydrophobic constituents. The lower part of the flat-shaped structure in the zone of the inlet openings for the water to be filtered has hydrophilic components for the passage of liquid. However, these measures do not suffice for the purpose of ensuring a non-hindered filling with water.
A filter cartridge with a fabric assembly is known from the EP 0 823 276 B1, said assembly being at least partially dome-shaped. The fabric section is secured to ribs.
The WO 98/05401 describes a filter cartridge with water inlet openings, water outlet openings and air outlet openings or windows, which are covered with a lattice that can consist of a synthetic material fabric. This fabric can be manufactured integrally with the cover.
The filter cartridge according to the WO 96/21621 also has water inlet openings and air outlet openings which are provided with a micro-porous paper.
From the U.S. Pat. No. 5,423,893 an injection-moulded lattice structure is known, which consists of inter-crossing webs. For technical reasons pertaining to the injection-moulding method, the lattice structure has ribs, which are circular-shaped in the cross-section, the diameter of said ribs is a multiple of the diameter of the webs. With these ribs, the entire lattice structure is subdivided into fields.
DE 197 44 361 describes a synthetic material filter with a filter lattice having a plurality of small passage openings. In order to create a synthetic material filter that can be manufactured in an injection-moulding process, the filter lattice consists of a first layer of ribs parallel to one another and a second layer of ribs parallel to one another, which cross the ribs of the first layer, both layers being located in two surfaces adjacent to one another and the inter-crossing ribs of the two surfaces are joined together at their crossing points. Therefore, the ribs or webs are located in two different planes.
These lattice structures also have the disadvantage that delays or even blockages can occur at the starting phase of the filling.